Making a UV projector for alt-process prints

[imgprojts]

Since the negatives are 4", how about these thin 5" gorilla glass windows with AR coatings?

5mm Dia., 1.10mm Thick Uncoated, Gorilla Glass® Window

TECHSPEC Gorilla Glass Windows are used as great protective covers for electronic displays in consumer and industrial systems. ✓ Shop now with Edmund Optics!

www.edmundoptics.com

Its 90% transmission in the UV range. So you'll drop 20% only.

 

[AndrewBurns]

This is where your light source matter a lot. You have to make it into a point-like source or you'll get ghosting. If you apply an aperture after the lens you can clean up some of it. But really the best thing to do is to focus the beam to a point and put an aperture right at that point. It will have a similar effect regardless of where you do it, but the effect will be strongest with less power loss if you have access to the focus point. I think. Its just a guess.This it will increase your exposure time but you'll get sharpness back.

Well this is the same light source and the same lens aperture as I was previously using with the LCD screen and I was perfectly happy with the sharpness I was getting from that combination there. I suppose one difference now is that the LED array is proportionally larger than the negative and lens entrance pupil as both of those got smaller when I went from the LCD to film, so that might make a difference? I'm trying to avoid reducing optical power to the paper as that will hurt my DAS carbon dmax again, but there could be some scope to use a smaller light source now that I've moved away from the LCD as the current one is probably wasted.

Would it help to sandwich the negative between two pieces of glass, glue it to the glass, or just use a glass plate directly?

Ideally I don't want to thermally insulate the negative too much because it will still be getting hot with how much power is going through it, but I have been thinking about putting a single glass plate behind the negative so that one face is still exposed to the cooling air from the fan but there's something rigid behind it to stop it flapping.

Since the negatives are 4", how about these thin 5" gorilla glass windows with AR coatings?

5mm Dia., 1.10mm Thick Uncoated, Gorilla Glass® Window

TECHSPEC Gorilla Glass Windows are used as great protective covers for electronic displays in consumer and industrial systems. ✓ Shop now with Edmund Optics!

www.edmundoptics.com

Its 90% transmission in the UV range. So you'll drop 20% only.

What you linked to is actually a 5mm diameter circle, however they do make a 150x150mm square too. I'm not sure how realistic of a concern it is but I believe people normally need some kind of anti-newton ring coating on glass if it's going to be directly in-contact with a negative to prevent interference patterns.